The rotary process for producing fibers is well known. Basically, it involves delivering a stream of molten or liquified material capable of being fiberized to a spinning rotor or disc and allowing centrifugal force to cause the material to extrude through small orifices in the disc sidewall. The resulting fibers are further attenuated and directed downwardly toward a moving collection belt or chain by a blast of air from nozzles or orifices in an air ring surrounding the fiberizing disc. The column of falling fibers is sprayed with binder which is later cured when the collected fibers are moved through an oven.
If the movement of the column of fibers is unaltered it converges at a point in its downward path to a minor diameter. The primary reason for this phenomenon is that the cylinder of high velocity air leaving the air ring orifices draws air from both inside and outside the cylinder. The inspiration of air inside the air cylinder creates a low pressure zone beneath the spinner disc, and the two pressure zones do not find equilibrium until they reach a point between the bottom of the spinner disc and the collection chain. The location of the minor diameter is affected by a number of factors, including the velocity of the air from the air ring and the static air pressure surrounding the column. The resulting well-defined relatively small column diameter permits precise deposition of fibers onto the collecting surface. On the other hand, it tends to facilitate the amassing of individual fibers into ropey bundles, resulting in many voids throughout the product due to poor fiber density distribution. Also, such a column has a high velocity which aggravates blowback around the collection chamber walls which in multi-spinner chambers can further deteriorate fiber density distribution. A glass fiber blanket product produced in this manner, for example, has less than optimal thermal insulating and tensile strength properties.
Because many of the properties of fibrous products produced by the rotary process are limited by the properties of the base fibers themselves or by the types and amounts of liquid binder that can be applied, it would at times be beneficial to modify the products in order to alter or enhance those properties. For example, it would at times be desirable to introduce additives to fibrous products for a variety of reasons. A major problem encountered in introducing additive materials, however, is the difficulty in uniformly distributing the materials throughout the fibrous matrix. If liquid additives are not sticky, they will not readily adhere to the fibers when sprayed onto the fiber column as it moves toward the collection surface. If liquid additives are sprayed onto an already formed fibrous mass, it is difficult to uniformly disperse them throughout the mass. To attempt to overcome these problems by introducing additives in solid rather than liquid form creates even more difficult problems. Solids cannot readily be introduced to a fibrous layer, nor does the present state of the art permit introducing them to the fibers as they move toward the collection surface.
It would be desirable to provide a method and means for better controlling the shape of the fiber column during production of fibers by the rotary process, while at the same time being able to introduce additive materials in such a way that they are uniformly distributed throughout the product. Further, the method of introduction should be such that it does not adversely affect the production of the base fibers or interfere with the collection and depositing of the produced fibers. In addition, the cost of introducing additives should be minor so as not to be a deterrent to the additive project. Neither should the method interfere with the introduction of liquid binder to the fibers.